The goal of this project is to investigate the role of a newly discovered postsynaptic protein, Shank, in the regulation of dendritic spine morphology and cytoskeleton. Local electrical stimulation induces growth of dendritic spines, suggesting that synaptic activity directly modulates neuronal architecture and circuitry. The molecular basis for these activitydependent changes is not known, but probably involves postsynaptic proteins that interact with receptors and/or cytoskeletal elements. Shank acts as a putative scaffold for multiple glutamate receptor subtypes and also binds to the actinbinding protein cortactin, which has been implicated in dynamic cytoskeletal rearrangement and translocates to synapses in response to glutamate. This study examines the role of Shank in the regulation of dendritic spines and its in vivo function through three specific aims. First a combination of cell biological, biochemical, and dominant inhibitory approaches will be used to determine the mechanism for glutamateregulated cortactin translocation to synapses, and to identify if Shankcortactin interaction is required for this response. Second, how Shank induces spine growth will be studied by structurefunction analysis. Finally, a genetic approach, generation of a Shank1 "knockout" mouse, will be used to investigate the role of Shank proteins in brain development, in postsynaptic receptor organization, and in learning and memory. The longterm goal of the candidate is to understand how aberrant synaptic transmission contributes to neurologic disease. Synapses are the signal processing units of the brain, and overexcitation of synapses by glutamate is thought to play a role in both acute neuronal injury (such as stroke and seizure) and chronic neurodegenerative conditions (including Huntington's disease, Parkinson's disease, and amyotrophic lateral sclerosis). Understanding how postsynaptic proteins, such as Shank, regulate activitydependent synaptic plasticity may shed light on mechanisms of glutamate toxicity. The immediate goal is to obtain training in the most uptodate techniques in molecular genetics, protein biochemistry, and cellular neurobiology, sponsored by Dr. Morgan Sheng, which will enable him to become a productive, independent molecular neurologist.